When utilizing electrostatic gripping on a transfer drum or belt, the voltage is typically applied at such a level that adherence of the paper to the drum is adequate. However, if the voltage is reduced below a certain level, some difficulty exists in adhering the paper to the drum or transfer belt. This is due to the fact that the paper has a tendency to lay flat, whereas the drum or transfer belt has an arcuate surface. Of course, after the paper has been on the drum for a sufficient amount of time, it will conform to the shape of the surface. Unfortunately, high speed copiers at present do not allow the paper to reside on the drum for very long.
In electrophotographic equipment, it is necessary to provide various moving surfaces which are periodically charged to attract toner particles and discharged to allow the toner particles to be transferred. At present, three general approaches have been embodied in products in the marketplace with respect to the drums. In a first method, the conventional insulating drum technology is one technology that grips the paper for multiple transfers. A second method is the semi-conductive belt that passes all the toner to the paper in a single step. The third technology is the single transfer to paper multi-pass charge, expose and development approach.
Each of the above approaches has advantages and disadvantages. The conventional paper drum technology has superior image quality and transfer efficiency. However, hardware complexity (e.g., paper gripping, multiple coronas, etc.), media variability and drum resistivity add to the cost and reduce the reliability of the equipment. By comparison, the single transfer paper-to-paper system that utilizes belts has an advantage of simpler hardware and more reliable paper handling. However, it suffers from reduced system efficiency and the attendant problems with belt tracking, belt fatigue and handling difficulties during service. Furthermore, it is difficult to implement the belt system to handle multi-pass to paper configuration for improved efficiency and image quality. The third technique, the single transfer-to-paper system, is operable to build the entire toner image on the photoconductor and then transfer it. This technique offers simple paper handling, but at the cost of complex processes with image quality limitations and the requirement that the photoconductor surface be as large as the largest image.